Visible-light-induced radical cascade cyclization: a catalyst-free synthetic approach to trifluoromethylated heterocycles

• Chuan Yang,
• Wei Shi,
• Jian Tian,
• Lin Guo,
• Yating Zhao and
• Wujiong Xia

Beilstein J. Org. Chem. 2024, 20, 118–124, doi:10.3762/bjoc.20.12

• Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, China 10.3762/bjoc.20.12 Abstract A visible-light-promoted research protocol for constructing dihydropyrido[1,2-a]indolone skeletons is herein described proceeding through a cascade cyclization mediated by trifluoromethyl

• enables a rapid access to heterocycles containing a trifluoromethyl group. Keywords: cascade reaction; indole derivatives; photocatalysis; radical chain process; trifluoromethylation; Introduction Dihydropyrido[1,2-a]indolone (DHPI) skeletons are commonly found in natural products and pharmaceutical

• ], Friedel–Crafts acylation [12], radical cascade reactions [2][13], and photoinduced radical cyclizations [14][15][16][17]. However, these methods often suffer from drawbacks such as harsh reaction conditions and the requirement of transition-metal catalysts. Although photocatalyzed cyclization reactions

Cycloaddition reactions of heterocyclic azides with 2-cyanoacetamidines as a new route to C,N-diheteroarylcarbamidines

• Pavel S. Silaichev,
• Tetyana V. Beryozkina,
• Vsevolod V. Melekhin,
• Valeriy O. Filimonov,
• Andrey N. Maslivets,
• Vladimir G. Ilkin,
• Wim Dehaen and
• Vasiliy A. Bakulev

Beilstein J. Org. Chem. 2024, 20, 17–24, doi:10.3762/bjoc.20.3

• , entries 2‒7) showed that the use of 100 mol % of DBU is optimal for the selective synthesis of triazole 3a in high yield (Table 1, entries 4 and 5). A study of the reaction medium revealed that common organic solvents are highly efficient for this cascade reaction (Table 1, entries 1‒11). Among the

Synthesis of N-acyl carbazoles, phenoxazines and acridines from cyclic diaryliodonium salts

• Nils Clamor,
• Mattis Damrath,
• Thomas J. Kuczmera,
• Daniel Duvinage and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2024, 20, 12–16, doi:10.3762/bjoc.20.2

• efficient method to synthesize N-acyl carbazoles from readily available iodolium salt and amides via a ring-opening/intramolecular coupling cascade (Scheme 1c) [20][21][22][23][24][25][26][27][28][29][30]. Our group recently explored principle synthetic pathways of hetero- and carbocyclic 5- and 6-membered

Anion–π catalysis on carbon allotropes

• M. Ángeles Gutiérrez López,
• Mei-Ling Tan,
• Giacomo Renno,
• Augustina Jozeliūnaitė,
• J. Jonathan Nué-Martinez,
• Javier Lopez-Andarias,
• Naomi Sakai and
• Stefan Matile

Beilstein J. Org. Chem. 2023, 19, 1881–1894, doi:10.3762/bjoc.19.140

• catalysis. Moreover, epoxide opening polyether cyclizations are among the most impressive cascade reactions in nature [71][72][73]. Best known is the hypothetical cascade XII in the biosynthesis of brevetoxin B [74]. It affords eleven fused ethers by violating the Eschenmoser–Dunitz–Baldwin guidelines [75

• ][76][77][78] in every step. Among the Baldwin compatible examples from nature, the cascade XIII leading to monensin A is arguably the most popular [79]. On anion–π catalysts other than carbon allotropes, up to four epoxides 34 have been cyclized into the monensin-like tetra-THF 35 as outlined in

• states IX and X. Primary anion–π autocatalysis on monofunctional fullerene 31, with catalytic and autocatalytic rate enhancements, representative cascade cyclizations with anti-Baldwin (XII) and Baldwin (XIII) selectivity in nature, and primary anion–π autocatalysis of cascade cyclization XIV on

Synthetic approach to 2-alkyl-4-quinolones and 2-alkyl-4-quinolone-3-carboxamides based on common β-keto amide precursors

• Yordanka Mollova-Sapundzhieva,
• Plamen Angelov,
• Danail Georgiev and
• Pavel Yanev

Beilstein J. Org. Chem. 2023, 19, 1804–1810, doi:10.3762/bjoc.19.132

• cascade [45], and base-promoted annulations with isatoic anhydrides [46]. Many other contributions in this field up to 2019 have been extensively reviewed [47][48][49], with special attention to the total synthesis and functional analysis of 2-alkyl-4-quinolones as microbial signaling molecules [50][51

Recent advancements in iodide/phosphine-mediated photoredox radical reactions

• Tinglan Liu,
• Yu Zhou,
• Junhong Tang and
• Chengming Wang

Beilstein J. Org. Chem. 2023, 19, 1785–1803, doi:10.3762/bjoc.19.131

• construction of these scaffolds [28][29][30][31], and one of the most efficient approaches is the cascade cyclization strategy [29][30][31]. Xu, Li, Wei and their co-workers successfully devised a series of highly regioselective iodide/phosphine synergistically catalyzed photocatalytic cascade annulations for

• -heterocycles. Recently, independent research groups led by Li, Yang, and Patureau separately disclosed a novel approach to 3,3-disubstituted oxindoles 43 through an iodide/phosphine-catalyzed visible-light-mediated decarboxylative radical cascade cyclization of N-arylacrylamides 42 (Scheme 18) [35][36

• ]. Importantly, these methodologies could also be smoothly extended to the synthesis of isoquinolinediones, which borne a quaternary carbon center. Furthermore, Yatham and his colleagues unveiled the first NaI/PPh3-mediated photocatalytic decarboxylative cascade cyclization of 2-isocyanobiaryls 44 with alkyl N

Trifluoromethylated hydrazones and acylhydrazones as potent nitrogen-containing fluorinated building blocks

• Zhang Dongxu

Beilstein J. Org. Chem. 2023, 19, 1741–1754, doi:10.3762/bjoc.19.127

• a surrogate of acetylene reacted with trifluoroacetonitrile imine to form 1-aryl-3-trifluoromethylpyrazoles, followed by a series of cascade annulation/dehydration/ring contraction reactions when treated with p-TsCl [65] (Scheme 10b). The chemistry of pyrazoles with a fluorine or a fluoroalkylated

• ], trifluorinated α-methylene-γ-lactams [99][100], and β-trifluoromethyl-β-acylhydrazonyl carbonyl compounds [101] (Scheme 15). Among these fluorinated products, the trifluoromethylated homoallylic acylhydrazines were easily transformed to CF3-substituted pyrazolines and 1,6-dihydropyridazines via a cascade

• . [3 + 2] Cycloadditions of difluoromethylated hydrazonoyl halides. Preparation and early applications of trifluoromethylated acylhydrazones. 1,2-Nucleophilic addition reactions of trifluoromethylated acylhydrazones. Cascade oxidation/cyclization reactions of trifluoromethylated homoallylic

A series of perylene diimide cathode interlayer materials for green solvent processing in conventional organic photovoltaics

• Kathryn M. Wolfe,
• Shahidul Alam,
• Eva German,
• Fahad N. Alduayji,
• Maryam Alqurashi,
• Frédéric Laquai and
• Gregory C. Welch

Beilstein J. Org. Chem. 2023, 19, 1620–1629, doi:10.3762/bjoc.19.119

• detrimental to device performance and long-term stability. Second, efficiency is increased by tuning the frontier molecular orbitals to block holes by a deep highest occupied molecular orbital (HOMO) and by promoting electron cascade with a deep lowest unoccupied molecular orbital (LUMO). Third, CILs prevent

• candidates as they can form electron transporting films, have appropriate LUMO energy levels compatible with most photoactive acceptor molecules (LUMO levels residing between −3.5 eV to −4.0 eV) to promote electron cascade, have appropriate HOMO energy levels at −5.5 eV and below that serve to block hole

Unraveling the role of prenyl side-chain interactions in stabilizing the secondary carbocation in the biosynthesis of variexenol B

• Moe Nakano,
• Rintaro Gemma and
• Hajime Sato

Beilstein J. Org. Chem. 2023, 19, 1503–1510, doi:10.3762/bjoc.19.107

• in the cyclization reaction. The role of these prenyl side chains has been partially investigated, but remains elusive in the cyclization cascade. In this study, we focus on variexenol B that is synthesized from iso-GGPP, as recently reported by Dickschat and co-workers, and investigate the

• offer many valuable insights from a fundamental organic chemistry perspective. The terpene cyclization cascade generally involves a multistep domino-type reaction. Therefore, it is challenging to reveal the detailed reaction mechanism solely by an experimental method. To address this issue

• aspects. First, this cyclization cascade involves a prenyl side chain that do not participate in the cyclization cascade. This type of terpene compounds has already been reported, such as santalene, bergamotene, mangicol, etc. The idea that the reaction mechanism changes due to differences in the prenyl

Functions of enzyme domains in 2-methylisoborneol biosynthesis and enzymatic synthesis of non-natural analogs

• Binbin Gu,
• Lin-Fu Liang and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2023, 19, 1452–1459, doi:10.3762/bjoc.19.104

• model was proposed that proceeds through the S-adenosylmethionine (SAM) dependent methylation of geranyl diphosphate (GPP) to 2-methyl-GPP (2-Me-GPP), followed by a terpene cyclisation to 1 (Scheme 1A) [10]. The cyclisation cascade requires isomerisation to (R)-2-methyllinalyl diphosphate [22], followed

Functional characterisation of twelve terpene synthases from actinobacteria

• Anuj K. Chhalodia,
• Houchao Xu,
• Georges B. Tabekoueng,
• Binbin Gu,
• Kizerbo A. Taizoumbe,
• Lukas Lauterbach and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2023, 19, 1386–1398, doi:10.3762/bjoc.19.100

• either through diphosphate abstraction (for type I terpene synthases) or protonation of the substrate (type II terpene synthases). The resulting cationic species can then react in a cascade reaction via a series of cationic intermediates involving cyclisations, hydride or proton shifts, and skeletal

Acetaldehyde in the Enders triple cascade reaction via acetaldehyde dimethyl acetal

• Alessandro Brusa,
• Debora Iapadre,
• Maria Edith Casacchia,
• Alessio Carioscia,
• Giuliana Giorgianni,
• Giandomenico Magagnano,
• Fabio Pesciaioli and
• Armando Carlone

Beilstein J. Org. Chem. 2023, 19, 1243–1250, doi:10.3762/bjoc.19.92

• organic synthesis to build complex scaffolds starting from simple starting materials. The Enders three-component cascade reaction was a cornerstone in the field and a plethora of organocatalyzed cascade reactions followed. However, acetaldehyde was not shown as a successful reaction partner, probably

• because of its high reactivity. Herein, we report the Enders-type cascade reaction using acetaldehyde dimethyl acetal, as a masked form of acetaldehyde. This strategy directly converts acetaldehyde, nitroalkenes and enals into stereochemically dense cyclohexenals in good yield and excellent

• enantioselectivity. Keywords: acetaldehyde; acetaldehyde dimethyl acetal; cascade reaction; multicomponent reaction; organocatalysis; Introduction Multicomponent reactions (MCRs) are chemical processes that involve three or more compounds, in which the product contains all the atoms of the reagents, except for

Selective construction of dispiro[indoline-3,2'-quinoline-3',3''-indoline] and dispiro[indoline-3,2'-pyrrole-3',3''-indoline] via three-component reaction

• Ziying Xiao,
• Fengshun Xu,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2023, 19, 1234–1242, doi:10.3762/bjoc.19.91

• substituent. A plausible reaction mechanism is proposed to explain the formation of the different spirooxindoles. Keywords: cascade reaction; dimedone; isatin; 3-methyleneoxindole; multicomponent reaction; spirooxindole; Introduction Spirooxindole is one important privileged structural skeleton and is found

• spirooxindoles, in which the in situ-generated Michael adduct of 3-ethoxycarbonylmethyleneoxindole underwent a Mannich reaction and annulation reaction with in situ-generated aldimines (reaction 1 in Scheme 1) [50][51]. Tanaka reported chiral quinidine derivative-catalyzed Michael–Henry cascade reactions of

• , 1526, 1545, 1368, 1285, 1145, 1025, 956, 882 cm−1; HRMS (ESI-TOF): [M + H]+ calcd. for C48H44ClN3O5, 760.2937; found, 760.2921. Crystal structure of dispiro compound 3a. Crystal structure of compound 4a. Representative cascade reactions of Michael adducts of 3-methyleneoxindoles. Proposed reaction

Radical ligand transfer: a general strategy for radical functionalization

• David T. Nemoto Jr,
• Kang-Jie Bian,
• Shih-Chieh Kao and
• Julian G. West

Beilstein J. Org. Chem. 2023, 19, 1225–1233, doi:10.3762/bjoc.19.90

• proposed to follow one of two pathways: formation of a carbocation through RPC followed by nucleophilic attack or direct RLT from a redox-active metal complex. Preliminary evidence for a radical decarboxylation/RLT cascade was reported in 1965, when Kochi demonstrated decarboxylative chlorination of

Unravelling a trichloroacetic acid-catalyzed cascade access to benzo[f]chromeno[2,3-h]quinoxalinoporphyrins

• Chandra Sekhar Tekuri,
• Pargat Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2023, 19, 1216–1224, doi:10.3762/bjoc.19.89

Enabling artificial photosynthesis systems with molecular recycling: A review of photo- and electrochemical methods for regenerating organic sacrificial electron donors

• Grace A. Lowe

Beilstein J. Org. Chem. 2023, 19, 1198–1215, doi:10.3762/bjoc.19.88

• that [CpRh(bpy)(H2O)]2+ could slowly produce formate, a key biocatalytic intermediate, in the absence of the enzymes but they validated their system by proving that overall the formate production and conversion to methanol by the biocatalytic enzyme cascade far outcompeted any side-reactions. Ishitani

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

• partners. The scope of the protocol was further expanded to a radical cyclization/aminocarbonylation cascade reaction yielding the bis-carbonylated α-keto amide 26h in 31% yield. 2.1.2 C(sp3)–X activation: The generation of alkyl radicals using alkyl halides as precursors proves very challenging due their

Synthesis of imidazo[4,5-e][1,3]thiazino[2,3-c][1,2,4]triazines via a base-induced rearrangement of functionalized imidazo[4,5-e]thiazolo[2,3-c][1,2,4]triazines

• Dmitry B. Vinogradov,
• Alexei N. Izmest’ev,
• Angelina N. Kravchenko,
• Yuri A. Strelenko and
• Galina A. Gazieva

Beilstein J. Org. Chem. 2023, 19, 1047–1054, doi:10.3762/bjoc.19.80

• [2,3-c][1,2,4]triazines was synthesized via a cascade sequence of hydrolysis and skeletal rearrangement of imidazo[4,5-e]thiazolo[2,3-c][1,2,4]triazin-7(8H)-ylidene)acetic acid esters in methanol upon treatment with excess KOH. Imidazo[4,5-e]thiazolo[3,2-b][1,2,4]triazin-6(7H)-ylidene)acetic acid

• ). Conclusion In summary, routes for the selective formation of various derivatives of the new heterocyclic system, imidazo[4,5-e][1,3]thiazino[2,3-c][1,2,4]triazine, were found during the cascade processes of alkaline hydrolysis of the ester group in functionalized derivatives of imidazo[4,5-e]thiazolo[3,2-b

Synthesis of tetrahydrofuro[3,2-c]pyridines via Pictet–Spengler reaction

• Elena Y. Mendogralo and
• Maxim G. Uchuskin

Beilstein J. Org. Chem. 2023, 19, 991–997, doi:10.3762/bjoc.19.74

• -c]pyridines. Moreover, multistep cascade processes with the simultaneous construction of several cores were described, where the key step is the generation of an acyliminium cation and the Pictet–Spengler cyclization [30][31][32], including solid-phase synthesis [33][34][35]. Another route for the

Aromatic C–H bond functionalization through organocatalyzed asymmetric intermolecular aza-Friedel–Crafts reaction: a recent update

• Anup Biswas

Beilstein J. Org. Chem. 2023, 19, 956–981, doi:10.3762/bjoc.19.72

• . The products 16 were achieved with excellent enantioselectivites which were attributed to an attractive interaction between the indole ring and the anthracene substituent of the catalyst’s framework (Scheme 5) [29]. In 2018, Piersanti and co-workers developed a phosphoric acid-catalyzed cascade

• utilizing cyclic N-sulfimines as electrophiles. Aza-Friedel–Crafts reaction involving N-unprotected imino ester as electrophile. Aza-Friedel–Crafts and lactonization cascade. One-pot oxidation and aza-Friedel–Crafts reaction. C1 and C2-symmetric phosphoric acids as catalysts. Aza-Friedel–Crafts reaction

Photoredox catalysis enabling decarboxylative radical cyclization of γ,γ-dimethylallyltryptophan (DMAT) derivatives: formal synthesis of 6,7-secoagroclavine

• Alessio Regni,
• Francesca Bartoccini and
• Giovanni Piersanti

Beilstein J. Org. Chem. 2023, 19, 918–927, doi:10.3762/bjoc.19.70

• Alessio Regni Francesca Bartoccini Giovanni Piersanti Department of Biomolecular Sciences, University of Urbino, Carlo Bo Piazza Rinascimento 6, 61029 Urbino, PU, Italy 10.3762/bjoc.19.70 Abstract An unusual photoredox-catalyzed radical decarboxylative cyclization cascade reaction of γ,γ

• different classes of ergot alkaloids. (b) and (c) Strategies for the photoredox-catalyzed radical decarboxylative cyclization cascade reaction of DMAT derivatives (this work). Proposed reaction mechanism for photoredox-catalyzed radical decarboxylative cyclization. Proposed reaction mechanism for photoredox

Facile access to 3-sulfonylquinolines via Knoevenagel condensation/aza-Wittig reaction cascade involving ortho-azidobenzaldehydes and β-ketosulfonamides and sulfones

• Ksenia Malkova,
• Andrey Bubyrev,
• Stanislav Kalinin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2023, 19, 800–807, doi:10.3762/bjoc.19.60

• have developed a new convenient protocol for the synthesis of 3-sulfonyl-substituted quinolines (sulfonamides and sulfones). The approach is based on a Knoevenagel condensation/aza-Wittig reaction cascade involving o-azidobenzaldehydes and ketosulfonamides or ketosulfones as key building blocks. The

• quinolines (sulfonamides and sulfones) (Figure 2b). Herein, we report the successful implementation of this approach. Results and Discussion The Knoevenagel condensation/aza-Wittig reaction cascade was used for the preparation of 3-sulfonyl-substituted quinolines. The process proceeds in a domino fashion

• synthesis of 3-sulfonyl-substituted quinolines (sulfonamides and sulfones). The approach is based on a Knoevenagel condensation/aza-Wittig reaction cascade for the quinoline core assembly. Hence, o-azidobenzaldehyde, ketosulfonamide or ketosulfone were utilized as key building blocks. The method devised

Nucleophile-induced ring contraction in pyrrolo[2,1-c][1,4]benzothiazines: access to pyrrolo[2,1-b][1,3]benzothiazoles

• Ekaterina A. Lystsova,
• Maksim V. Dmitriev,
• Andrey N. Maslivets and
• Ekaterina E. Khramtsova

Beilstein J. Org. Chem. 2023, 19, 646–657, doi:10.3762/bjoc.19.46

• to the PBTA scaffold is an annulation of benzothiazoles with a pyrrole moiety (Scheme 1). It includes intramolecular cyclizations of benzothiazoles bearing a 3'-chloro substituent at C2 position (Scheme 1, entries 1 and 2) [5][6][7], intramolecular catalytic carbene cascade reactions of propargyl 1,3

• ] and reactions of 3-acyl-2,3-dihydro-1,3-benzothiazole-2-carbonitriles with acetylenedicarboxylate (Scheme 1, entry 9) [4]. The second group of approaches to the PBTA scaffold is an annulation of o-aminothiophenol with a pyrrolothiazole moiety (Scheme 2). It includes catalytic cascade reactions of o

• -aminothiophenol with donor–acceptor cyclopropanes (Scheme 2, entry 10) [27], condensations of o-aminothiophenol with 4-oxo acids or their derivatives (Scheme 2, entry 11) [2][28][29][30][31] and cascade reactions of o-aminothiophenol, furfural and anhydrides of 2,3-unsaturated carboxylic acids (Scheme 2, entry 12

Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

• Péter Kisszékelyi and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44

• , crop-protecting agents, or advanced materials. Their syntheses often involve numerous reaction steps requiring laborious isolation and intermediate product purification steps. An important strategy for improving syntheses’ effectiveness is the concept of domino reactions, cascade, or tandem reactions

• the enolate intermediate in a cascade sequence, including borylation, aldol reaction, and finally oxidation (Scheme 36). The product 146 containing three consecutive stereocenters was obtained in a dr of 6.5 to 1 and with good yield and enantioselectivity. Lam and co-workers described a highly

• structurally different Michael acceptors were successfully applied. Their work also included a 3 mmol scale-up (62%, 87% ee, dr >20:1) and various derivatizations of the Mannich products. Furthermore, they have also attempted a multi-electrophile cascade reaction, which harnesses the nucleophilic nature of the

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

• shed light on future directions for further development in this field. Keywords: bicyclic alkenes; cascade; catalysis; domino; transition-metal-catalyzed; Introduction A well-orchestrated sequence of events – cascade, also known as domino, tandem, and sequential reactions, constitutes a fascinating

• this section, showcasing several diverse nickel-catalyzed domino reactions. In 2001, Rayabarapu and co-workers investigated the Ni-catalyzed ring-opening/cyclization cascade of heterobicyclic alkenes 1 with alkyl propiolates 2 for the synthesis of coumarin derivatives 3 (Scheme 1) [28]. The reaction

• -opening/cyclization cascade of heterobicyclic alkenes 1 with β-iodo-(Z)-propenoates and o-iodobenzoates 9 (Scheme 2) [33]. The authors noted the ring-opening/cyclization cascade proceeded smoothly for a variety of heterobicyclic alkenes including both oxa- and azabenzonorbornadienes as well as